Generally, the present invention relates to a method and apparatus for positioning a stent within a body vessel, typically a blood vessel. The invention is particularly applicable to polymeric stents which though self expandable, typically have low radial strength. Due to differences in mechanical properties, self expanding, polymeric stents of a mesh design do not have the radial expansion force that metallic stents do. Because of this decreased radial force, polymeric stents seldomly completely expand against vessel walls by themselves. Complete expansion against the vessel wall is critical for proper stent implantation. The apparatus of the present invention was designed to ensure complete stent expansion. The elements of the apparatus are combined and arranged in such a way as to foster delivery, positioning, implantation and withdrawal with minimal trauma.
Stents are typically implanted within the vascular system to reinforce collapsing, partially occluded, weakened or under dilated sections of vessel. Stents have also been successfully implanted in urinary tracts and bile ducts to reinforce those body vessels. This invention is applicable in all of these situations.
In general, the typical procedure for implanting a self expanding stent is to first open the region of the vessel with a balloon catheter and then place the stent in a position bridging the weakened the portion of the vessel. Positioning of the stent may be followed by the technique known as the "Swiss Kiss" in which a separate balloon catheter is positioned within the stent and expanded to radially expand the stent for implantation.
Many patents refer to the construction and design of both stents as well as apparatus for positioning the stent within a vessel. One such patent is U.S. Pat. No. 4,140,126 to Chaudhury which issued Feb. 20, 1979. This patent disclosures a technique for positioning an elongated cylinder at a region of an aneurysm to avoid failure of the blood vessel wall. The patent discloses a cylinder that expands to its implanted configuration after insertion with the aid of a catheter.
A patent to Dotter, U.S. Pat. No. 4,503,569 which issued Mar. 12, 1985 discloses a spring stent which expands to an implanted configuration with a change in temperature. The spring stent is implanted in a coil orientation and heated to cause the spring to expand.
U.S. Pat. No. 4,733,665 to Palmaz which issued Mar. 29, 1988, discloses a number of stent configurations for implantation with the aid of a catheter. The catheter includes a mechanism for mounting and retaining the vascular prosthesis or stent, preferably on an inflatable portion of the catheter. The stent is implanted by positioning it within the blood vessel and monitoring its position on a viewing monitor. Once the stent is positioned as desired, the catheter is expanded and the stent is separated from the catheter body. The catheter can then be withdrawn from the subject, leaving the stent in place within the blood vessel.
U.S. Pat. No. 5,019,090 to Pinchuk, issued May 28, 1991, discloses delivery of a stent within a guiding catheter in combination with a dilation balloon in which the balloon is distally positioned relative to the stent.
U.S. Pat. No. 4,886,062 to Wiktor issued Dec. 12, 1989 and assigned to the same assignee as is the subject invention, discloses a stent carried on a dilation balloon which is positioned via a guiding catheter.